Various methods to extract coal from the earth are well known. Depending on many factors such as the location and configuration of the coal seam and its concentration, it may not be economically practical to mine the coal by conventional methods employing cutting heads, explosives, water jets, etc. Generally, when the coal seams are too narrow to mine economically, or are located in areas where conventional coal mining methods are impractical to use, the coal is left unmined. There is a large amount of coal in the United States which falls in this category and which could add substantially to our reserves if it could be extracted. We describe herein an alternative method of recovery whereby the coal is solubilized in situ by electrolysis and the pregnant solution pumped to the surface where it is then further processed into fuel or used for petrochemical processes.
In December 1981, a paper co-authored by us and entitled "Electrolytic Oxidation of Anthracite" was published in Volume 60 of the IPC Business Press journal "Fuel." As set forth therein, the electrolytic oxidation of bituminous and/or anthracite coal is known as a laboratory method. With these previous methods, two metallic electrodes were used with the coal slurry being circulated around the positive electrode. Normally, the electrodes were separated by a permeable membrane to keep the coal particles from contacting the negative electrode. In contrast to these prior art methods, our invention described herein employs a method without a separating membrane between the electrodes as the coal itself acts as the positive electrode. As a consequence, there is a very marked increase in the oxidation efficiency with our process over the prior art methods.
In the process of oxidation, the coal is converted to various complex carboxylic acids, the exact composition of which is not known. These carboxylic acids are soluble in basic solutions. During the electrolytic process, hydrogen gas is given off at the metallic electrode surface (negative electrode) and oxygen is evolved at the nearby coal surface which acts as a positive electrode. The carboxylic acids are valuable as starting materials for the synthesis of organic compounds and plastics, and the evolved gases can be used for their usual commercial applications. Thus, all the end products are useful and recoverable.
In contrast to performing the electrolysis in the laboratory as described in the above referred report, this invention involves doing the electrolysis in situ, i.e., in the coal seam itself, to recover the mentioned valuable products. Recovery of coal components by solution mining subsequent to electrolysis precludes the necessity of strip mining or conventional mining which can be both undesirable and, in many cases, uneconomical.